The present invention relates to a method and a device for half-duplex serial signal control with multibaud rates and multiconfigurations and, more specifically to a method and a device for half-duplex serial signal control with multibaud rates and multiconfigurations used on a network among at least one computer and other equipments from different manufacturers and using different communication speeds.
It is known that RS-232 communicates with a series of serial signals. In order to send a byte, several parts of the following are included:
start bit+data bit+parity bit+stop bit where start bit=1 bit
data bit=7 bits or 8 bits
parity bit=0 bit or 1 bit
stop bit=1 bit or 2 bits
The shortest length of the serial signal is 9 (=1+7+0+1) bits while the longest is 12 (=1+8+1+2). There are four possible configurations of the signal being sent: 9, 10, 11, and 12 bits. In practical applications, there is no preferred configuration. So the default configuration for data transmission among products made by each manufacturer might be different. The number of bytes transmitted in one second is called the baud rate. The specifications of baud rate differ among different equipment. The baud rate adopted by each manufacturer might not be the same and there is no universal agreement on baud rate in the industry. These limitations altogether make the networking between a PC and PLCs difficult. It is desirable to use the same products and the same communication speed.
By half-duplex communication, it means that the host computer and other equipment or instruments connected cannot receive and transmit at the same time. The data transmission is done in the request and answer fashion. The host computer sends an instruction and the equipment or instruments return a result. The activity of transmission and the activity of receiving cannot happen at the same time.
In the current industry, there are a lot of equipment or instruments that can be controlled via programmable logic controllers (PLC). In response to the demand for full automation, there is a need to link these PLCs in a network. PLCs usually come with RS-232 interface which can be configured to different addresses. They are qualified to link to one another in a network.
FIG. 1 shows the schematics of connecting several programmable logic controllers with multi RS-232 interface. A PC can use the RS-232 interface which has multiports to connect several PLCs. The PC can switch among the RS-232 ports so that at any moment, there is only one PLC that can communicate with the PC and each PLC can be controlled when the corresponding RS-232 port is selected in turns. The major drawback of this type of connection is the high cabling cost and the difficulty in system maintenance. The area of a factory is usually large, so the PLCs might be located far apart from each other. If all the PLCs are connected to the PC, lots of cables and hence the capital will be needed. With the cables hanging around in the factory, the system maintenance becomes more difficult.
FIG. 2 shows the schematics of connecting several programmable logic controllers with a four-wire RS-485 interface. A converter which works between RS-232 and four-wire RS-485 is used. The connection between the PC and the PLCs is done by four RS-485 wires. With this setup, both the cabling cost and the difficulty in system maintenance will be significantly reduced compared to the setup in FIG. 1. Each PLC in FIG. 2 responds only when the received instruction matches its address. If the PC sends an instruction to address #1, all the PLCs receive this instruction but only PLC#1 responds. Because only PLC#1 has the address #1, others do not. Similarly, the PC can send messages to #2, #3 É#m respectively, so all the PLCs can be controlled.
FIG. 3 shows the schematics of connecting several programmable logic controllers with a two-wire RS-485 interface. A converter which works between RS-232 and two-wire RS-485 is used. The connection between the PC and the PLCs is done by only two RS-485 wires. With this setup, the cost of cabling and the cost of system maintenance can be reduced by half, in comparison with FIG. 2. The operation principle in FIG. 3 is similar to that in FIG. 2. The main difference is that in FIG. 2, T+ and Txe2x88x92 send instructions while R+ and Rxe2x88x92 receive. In FIG. 3, D+ and Dxe2x88x92 can be used to send and receive. The RS-232/RS-485 converter and the RS-485 repeater in FIG. 3 are more complicated than those in FIG. 2. If the PLCs use a different baud rate and configuration, the RS-232/RS-485 converter and the RS-485 repeater can hardly do their job. This is why instruments or equipment from different manufacturers have problems in networking, especially if they are not purchased at the same time. For the time being, problems remain when using converters and repeaters in the above setup, no matter whether they are domestically manufactured or imported.
Accordingly, applicants have developed a method and a device for half-duplex serial signal control with multibaud rates and multiconfiguration.
In one form of the present invention, a method for half-duplex serial signal control with multibaud rates and multi-configuration is proposed. A new controlling approach utilizing the receiving/transmission signal control wire on the interface circuit is used on the network having multibaud rates and multiconfiguration. Instruments or equipments from different manufacturers can therefore connect to one another.
In another form of the present invention, a system for half-duplex serial signal control with multibaud rates and multiconfiguration includes a power circuit a, protective circuit a, RS-232 interface circuit a, RS-485 interface circuit and a logical control circuit. The serial signal is converted between the RS-232 and RS-485 interfaces in order to receive, transmit and repeat signals using only D+ and Dxe2x88x92 wires in the two-wire RS-485 network. A brand new method is used to regulate the signal in the receiving/transmission signal control wire on the interface circuit so that multibaud rates and multiconfiguration are allowed on the network. Instruments or equipment from different manufacturers or using different communication speed can thus connect with each other. The cost and the difficulty in maintenance can both be reduced.
With the traditional networking, PLCs from different manufacturers might have different baud rates and different configurations. Instead of two-wire RS-485, four-wire RS-485 is needed. The cost for material and maintenance which is significantly increased by at least double burdens the end users. The most important technical advantage of the present invention includes a new control approach which allows the PLCs on a two-wire RS-485 to have different baud rates and different configurations for RS-232 communication.